The insulin receptor has been studied in a variety of animal species including mammals, birds, amphibians, bony fish and cyclostomes. Despite nearly a half million years of divergent evolution, the insulin receptor in all of these species maintained remarkably similar binding properties, including saturability, reversibility, specificity, temperature and pH dependence, as well as negative cooperativity. In all the species the insulin receptor binds different insulin analogues in proportion with their relative insulin-like bioactivity. BIBLIOGRAPHIC REFERENCES: Ginsberg, B.H., Kahn, C.R., and Roth, J.: The Insulin Receptor of the Turkey Erythrocyte: Purification and Characterization of the Membrane Bound Erythrocyte: Purification and Characterization of the Membrane Bound Receptor. Biochem. Biophys. Acta 443: 227-242, 1976. Ginsberg, B.H., Kahn, C.R., and Roth, J.: The Insulin Receptor of the Turkey Erythrocyte: Similarity to Mammalian Insulin Receptors. Endocrinol. 100: 82-90, 1977.